Wheel balancers are commonly used in order to balance discs, disc shaped structures and vehicle wheels. Discs such as vehicle wheels are generally mounted to a hub connected to disc brakes or drum brakes which are generally circular in configuration. During the manufacturing process, the disc brakes or drum brakes are not manufactured perfectly round. Therefore, during rotation, the vehicle wheel will generally start to vibrate or chatter at elevated rotational speeds. This can be generally overcome by adding a weight to the vehicle wheel to minimize this vibration or chatter in a manner well-known to those persons skilled in the art. Accordingly, any rotating object or disc will produce a centrifugal force because of the asymmetric mass distribution when it rotates about its axis.
Wheel balancers are commonly used to measure imbalance values and position of a rotating object. This imbalance centrifugal force can bring on object vibration, both electrically and mechanically, as well as produce noise on mechanical vibration which can poorly affect the product's character and lifespan.
Therefore, a wheel balancer is usually used to inspect rotation object imbalance forces, including data range and position in industrial practices. Such balancing can improve the rotating object's mass distribution related to the axis and reduce vibration to the approved range so that it will improve the character of the rotation after corresponding compensation has been implemented.
Generally speaking, the principle utilized by common wheel balancers include the steps of:                Installing and fixing the imbalance object to the rotary axis of the wheel balancer;        Inputting the imbalance object's width, diameter and distance between the object and the wheel balancing machine;        Starting the wheel balancer to spin or rotate whereby during spinning an encoder and code wheel (which are generally fixed on the rotary axis) interfere to confirm the imbalance position in one or more piezoelectric devices utilized for testing imbalance values; and        Then utilizing a microprocessor in the calculation of imbalance values and position which will be displayed after the wheel balancer brakes all in the manner well known to those persons skilled in the art.        
Furthermore, the main structures for common wheel balancers include:                Electric Power Drive Device—main function is drive a rotary axis;        Rotary Axis and Base of Rotary Axis—main function is to support the rotary axis and drive the imbalance object to spin;        Signal Device—usually include a pair of piezoes whose main function is getting an imbalance weight value signal of the imbalanced object or disc; a code wheel and encoder are usually utilized whose main function is getting an imbalance position signal of the imbalanced object;        Microprocessor—main function is to deal with the signal from the signal device in order to confirm imbalance, weight and position; confirm whether the power drive device is separated from the rotary axis of the wheel balancer and confirm balance type and process;        Display Device—main function is to display an imbalance weight and position in order to confirm balance type and other information;        Brake Device—main function is to break the rotary axis of the wheel balancer.        
There are a variety of prior art wheel balancers in the marketplace which include the following:    1. A wheel balancer that has an AC or DC motor which drives a shaft about an axis of rotation by use of belt wheel and belt. The power to the motor is shut down when the rotating axis or its shaft rotates at a desired speed or rating speed. Examples of such traditional wheel balancers include wheel balancers available from Hofmann in Germany, CEMB in Italy and Hunter in the USA.    2. Wheel balancers with an AC or DC motor, which motor drives the rotary axis or shaft to rotate by friction between rollers or gears on the motor and the vehicle wheel through friction. The power supply to the motor is shut down when the rotary axis rotates at a desired speed or rating speed, in which event, the rotor or gear from the friction wheel to the wheel is disengaged and the rotary axes or shaft in the wheel balancer rotates by inertia. Examples of such traditional wheel balancers include wheel balancers from Corghi and Simply Faip in Italy.    3. Other traditional wheel balancers include fixing a rotor of an AC or DC motor directly on the rotary axis. The stator is outside the rotor and the motor directly drives the axis or shaft of the wheel balancer. The power supply is shut down when the rotary axes rotates at a desired or rating speed. Representative wheel balancers of this type are found through Coats in the USA.
Each of the three types of prior art wheel balancers described above include inefficiencies which effects the balancing of a vehicle wheel. For example, over time the belts utilized in the wheel balancers identified under paragraph 1 above will generally loosen after a period of usage and the balancing system will become unstable thereby reducing the precision of the balance. Moreover, wheel balancers of the type described in paragraph 2 above require complex mechanical and electro control circuits which are difficult to process and adjust. Furthermore, wheel balancers of the type described in paragraph 3 above also require complex mechanical and electronic control circuits making the process technologies and manufacturing processes, difficult and costly to operate.
There have been a number of prior art devices. For example U.S. Pat. No. 7,574,913 relates to a method for determining weight display thresholds for static and dynamic imbalances and correction weights on a rotating body such as a vehicle wheel assembly which vary with parameters of the rotating body, wheel and/or tire, and for displaying measured imbalances in relation to determine imbalance thresholds.
Another arrangement is disclosed in U.S. Pat. No. 4,502,328 which relates to a free spinning electronic wheel balancer.
Furthermore U.S. Pat. No. 4,480,472 relates to a dynamic electric wheel balancer for measuring the imbalance condition in a vehicle wheel and indicating the position and correction weights required for balancing the wheel in one or two plains. The wheel balancer contains a rotating shaft in order to make the dynamic measurements. The shaft is free-wheeling during measurement and is brought up to a predetermined minimum RPM value through a motor and clutch arrangement.
Another wheel balancer is show in U.S. Pat. No. 6,854,329.
U.S. Pat. No. 6,799,460 teaches a wheel balancer that includes a shaft adapted for receiving a wheel assembly and rotating a wheel assembly; mounted thereon with a motor connected to the shaft, rotating the shaft about its longitudinal axis, thereby rotating the wheel assembly.
Finally U.S. Pat. Nos. 6,546,635 and 6,439,049 show other wheel balancer arrangement.
It is an aspect of this invention to provide a device to balance a disc, comprising: a shaft disposed for rotation about an axis having: one end adapted to coaxially receive the disc, and an opposite end including rotor means; stator means to magnetically drive the rotor means, shaft and disc about the axis; and means for determining imbalance in the disc.
It is another aspect of this invention to provide a balancer for a wheel comprising: a frame; stator means supported by the frame; a shaft supported by the frame for rotating about an axis and having first and second axial spaced ends; a stub shaft coaxial presented at the first end for removable connection to the wheel; a rotor means coaxially connected to the second end and axially spaced from the stator means; power means associated with the stator means to generate an electromagnetic field between the stator means and the rotator means to rotate the shaft and wheel; means responsive to the rotation of the wheel for measuring and indicating imbalance of the rotating wheel.
A further aspect of this invention relates to a method for balancing a vehicle wheel connected at one end to a shaft rotating about an axis and having a rotor at the other end of said shaft comprising the steps of: powering a stator axially disposed adjacent the rotor so as to electromechanically drive the rotor, shaft and vehicle wheel about the axis of rotation.